Deduplication doesn't occur with `imports_granularity = "Item"

[djmarcin]

Describe the bug

Duplicate imports are not removed with imports_granularity = "Item" turned on.

To Reproduce

test.rs

use std::env;
use std::env;

fn main() {
  println!("{:?}", env::var("TEST"));
}

.rustfmt.toml

unstable_features = true
edition = "2018"
imports_granularity = "Item"

Run rustfmt test.rs

Expected behavior

Duplicate use std::env; should be removed. It is not.

Meta

• rustfmt version: rustfmt 1.4.36-nightly (7de6968 2021-02-07)
• From where did you install rustfmt?: asdf install with .tool-versions rust nightly-2021-02-17
• How do you run rustfmt: rustfmt, in VSCode

[calebcartwright]

Thanks for opening this! We'd actually just observed this recently as well (#4716 (comment)) so good to have an issue to track 👍

[calebcartwright]

For anyone interested in working on this, would suggest starting here given the current code structure. Note that the trees are not yet sorted at this point, as sorting conditionally happens a bit later on depending on the user specified value for the reorder_imports option. We need to dedupe regardless of the value of reorder_imports

rustfmt/src/formatting/imports.rs

Lines 185 to 201 in 74768b7

	pub(crate) fn flatten_use_trees(use_trees: Vec<UseTree>) -> Vec<UseTree> {
	use_trees
	.into_iter()
	.flat_map(UseTree::flatten)
	.map(|mut tree| {
	// If a path ends in `::self`, rewrite it to `::{self}`.
	if let Some(UseSegment::Slf(..)) = tree.path.last() {
	let self_segment = tree.path.pop().unwrap();
	tree.path.push(UseSegment::List(vec![UseTree::from_path(
	vec![self_segment],
	DUMMY_SP,
	)]));
	}
	tree
	})
	.collect()
	}

[zaki-yama]

@calebcartwright
Hello! May I try this?

[calebcartwright]

@calebcartwright
Hello! May I try this?

Sure! However, I think @davidBar-On may have beaten you to it in #4737. Will leave it to the two of you to sort who wants to work on it.

[davidBar-On]

@zaki-yama, I suggest to see if my approach in PR #4737 to resolve the issue is accepted. If not, I have no problem that you will take over. (Usually I am not trying to resolve new help wanted assigned issues, but this one is somewhat related to #4681 which I submitted a PR for.)

[zaki-yama]

@calebcartwright @davidBar-On
Thank you for replying.
Sure! Since I'm new to try the issue in this repository, I'll see and learn from #4737.
Also, I'll see other help wanted or good first issue labeled issues.